Ruby Language QuickRef
General Syntax Rules
Reserved Words
Types
Basic types are numbers, strings, ranges, regexen, symbols, arrays, and hashes. Also included are files because they are
used so often.
Numbers
Strings
In all of the %() cases below, you may use any matching characters or any single character for delimiters. %[], %!!,
%@@, etc.
Backslashes
\t (tab), \n (newline), \r (carriage return),
\f (form feed), \b (backspace), \a (bell),
\e (escape), \s (whitespace), \nnn (octal),
\xnn (hexadecimal), \cx (control x),
\C-x (control x), \M-x (meta x),
\M-\C-x (meta control x)
Here Docs
<<identifier # interpolation
<<"identifier" # interpolation
<<'identifier' # no interpolation
<<-identifier # interpolation, indented end
<<-"identifier" # interpolation, indented end
<<-'identifier' # no interpolation, indented end
Symbols
A symbol (:symbol) is an immutable name used for identifiers, variables, and operators.
Ranges
1..10
'a'..'z'
(1..10) === 5 -> true
(1..10) === 15 -> false
# prints lines starting at 'start' and
# ending at 'end'
while gets
print if /start/../end/
end
class RangeThingy
def <=>(rhs)
# ...
end
def succ
# ...
end
end
range = RangeThingy.new(lower_bound) .. RangeThingy.new(upper_bound)
Regexen
/normal regex/[xim]
%r|alternate form|[xim]
Regex.new(pattern, options)
Arrays
[1, 2, 3]
%w(foo bar baz) # no interpolation
%W(foo #{bar} baz) # interpolation
Indexes may be negative, and they index backwards (-1 is the last element).
Hashes
{ 1 => 2, 2 => 4, 3 => 6 }
{ expr => expr, ... }
Files
Common methods include:
Mode Strings
Variables and Constants
$global_variable
@instance_variable
[OtherClass::]CONSTANT
local_variable
Pseudo-variables
Pre-defined Variables
Comments start with a pound/sharp (#) character and go to EOL.
Lines between ‘=begin’ and ‘=end’ are skipped by the interpreter.
Ruby programs are sequence of expressions.
Each expression is delimited by semicolons (;) or newlines unless obviously incomplete (e.g.
trailing ‘+’).
Backslashes at the end of line does not terminate expression.
alias and BEGIN begin break case
class def defined do else elsif
END end ensure false for if
in module next nil not or
redo rescue retry return self super
then true undef unless until when
while yield
123 1_234 123.45 1.2e-3
0xffff (hex) 0b01011 (binary) 0377 (octal)
?a ASCII character
?\C-a Control-a
?\M-a Meta-a
?\M-\C-a Meta-Control-a
'no interpolation'
"#{interpolation} and backslashes\n"
%q(no interpolation)
%Q(interpolation and backslashes)
%(interpolation and backslashes)
`echo command interpretation with interpolation and
backslashes`
%x(echo command interpretation with interpolation and
backslashes)
. any character except newline
[set] any single character of set
[^set] any single character NOT of set
* 0 or more previous regular expression
*? 0 or more previous regular expression (non greedy)
+ 1 or more previous regular expression
+? 1 or more previous regular expression (non greedy)
? 0 or 1 previous regular expression
| alternation
( ) grouping regular expressions
^ beginning of a line or string
$ end of a line or string
#{m,n} at least m but most n previous regular expression
#{m,n}? at least m but most n previous regular expression (non greedy)
\A beginning of a string
\b backspace (0x08, inside [] only)
\B non-word boundary
\b word boundary (outside [] only)
\d digit, same as[0-9]
\D non-digit
\S non-whitespace character
\s whitespace character[ \t\n\r\f]
\W non-word character
\w word character[0-9A-Za-z_]
\z end of a string
\Z end of a string, or before newline at the end
(?# ) comment
(?: ) grouping without backreferences
(?= ) zero-width positive look-ahead assertion (?! )
(?ix-ix) turns on/off i/x options, localized in group if any.
(?ix-ix: ) turns on/off i/x options, localized in non-capturing group.
File.join(p1, p2, ... pN) => “p1/p2/.../pN© platform independent paths
File.new(path, mode_string="r") => file
File.new(path, mode_num [, perm_num]) => file
File.open(filename, mode_string="r") {|file| block} -> nil
File.open(filename [, mode_num [, perm_num ]]) {|file| block} -> nil
IO.foreach(path, sepstring=$/) {|line| block}
IO.readlines(path) => array
r Read-only, starts at beginning of file (default mode).
r+ Read-write, starts at beginning of file.
w Write-only, truncates existing file to zero length or creates a new file for writing.
w+ Read-write, truncates existing file to zero length or creates a new file for reading
and writing.
a Write-only, starts at end of file if file exists, otherwise creates a new file for
writing.
a+ Read-write, starts at end of file if file exists, otherwise creates a new file for
reading and writing.
b Binary file mode (may appear with any of the key letters listed above). Only
necessary for DOS/Windows.
self the receiver of the current method
nil the sole instance of NilClass (represents false)
true the sole instance of TrueClass (typical true value)
false the sole instance of FalseClass (represents false)
__FILE__ the current source file name.
__LINE__ the current line number in the source file.
$! The exception information message set by ‘raise’.
$@ Array of backtrace of the last exception thrown.
$& The string matched by the last successful pattern match in this scope.
$` The string to the left of the last successful match.
$' The string to the right of the last successful match.
$+ The last bracket matched by the last successful match.
$1 The Nth group of the last successful match. May be > 1.
$~ The information about the last match in the current scope.
$= The flag for case insensitive, nil by default.
$/ The input record separator, newline by default.
$\ The output record separator for the print and IO#write. Default is nil.
$, The output field separator for the print and Array#join.
$; The default separator for String#split.
$. The current input line number of the last file that was read.
$< The virtual concatenation file of the files given on command line.
$> The default output for print, printf. $stdout by default.
$_ The last input line of string by gets or readline.
$0 Contains the name of the script being executed. May be assignable.
$* Command line arguments given for the script sans args.
$$ The process number of the Ruby running this script.
$? The status of the last executed child process.
$: Load path for scripts and binary modules by load or require.
$" The array contains the module names loaded by require.
$DEBUG The status of the -d switch.
$FILENAME Current input file from $<. Same as $<.filename.
$LOAD_PATH The alias to the $:.
$stderr The current standard error output.
$stdin The current standard input.
$stdout The current standard output.
$VERBOSE The verbose flag, which is set by the -v switch.
$-0 The alias to $/.
